1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, capable of controlling a throttle opening to obtain a target amount of intake air.
2. Description of the Related Art
Recently, there has been proposed a control apparatus for an internal combustion engine using an output shaft torque of an internal combustion engine (engine), which corresponds to a physical quantity directly acting on the control of a vehicle, as a requested value of a driving force from a driver or a vehicle side. In such a control apparatus for an internal combustion engine, good running performance is obtained by deciding the amount of air, the amount of fuel, and ignition timing corresponding to engine control quantities by using the output shaft torque as an output target value of the engine.
In addition, it is generally known that a control quantity which has the greatest influence on the engine output shaft torque among the engine control quantities is the amount of air. Therefore, for controlling the amount of air with high accuracy, the applicant of the present application has proposed a control apparatus for an internal combustion engine for calculating a target effective opening area of an intake system based on a target flow rate of intake air, an atmospheric pressure, an intake manifold pressure, and an intake air temperature and for outputting a target throttle opening from a correlation map which prestores a correlation between an effective opening area of the intake system and an opening of a throttle valve to control the throttle opening (for example, see Japanese Patent Application Laid-open No. 2007-239650; hereinafter, referred to as Patent Document 1).
However, in Patent Document 1, even at the same throttle opening, a variation is generated in an actual opening area or flow coefficient due to a manufacturing variation for each individual throttle body. Therefore, the flow rate of intake air varies for each throttle body. Moreover, a variation is also generated in the calculated opening area or effective opening area due to a variation between sensors for measuring the intake manifold pressure, the atmospheric pressure or the intake air temperature, or an error inherent in an estimation method.
As described above, there is a problem in that a variation is generated in the actual flow rate of intake air with respect to the target flow rate of intake air due to the variations between the throttle bodies, various sensors, and the like, or various estimation errors.
Therefore, in order to solve the above problem, the applicant of the present application has proposed throttle opening learning means for learning and correcting the relation between the effective opening area and the throttle opening to adequately achieve the target flow rate of intake air against the variation between the throttle bodies, various sensors, and the like or various estimation errors when the throttle opening for obtaining the target flow rate of intake air is to be calculated. The applicant of the present application has also proposed a method of storing a throttle learning value (for example, Japanese Patent Application Laid-Open No. 2008-057339; hereinafter, referred to as Patent Document 2).
According to Patent Document 2, a throttle learning value according to a ratio of distances between axis points before and after a target effective opening area and an actual effective opening area is added in at least one of a learning region corresponding to two axis points before and after the target effective opening area and a learning region corresponding to two axis points before and after the actual effective opening area on a correlation map for converting the effective opening area into the throttle opening. Then, the throttle learning value is stored.
FIG. 9 is an explanatory view of the throttle learning value calculated in Patent Document 2 which is the related art. As shown in FIG. 9, the relation of the throttle opening with respect to the actual effective opening area and a set correlation map deviate from each other in a crossing manner. The case where learning is performed in a learning region corresponding to two axis points before and after the actual effective opening area is now considered. In this case, the learning is performed in the same direction according to a ratio of the actual effective opening area to the axis point at the two axis points before and after the actual effective opening area. Therefore, when the learning is performed to cause one axis to get closer to the actual relation, the other axis consequently performs mislearning in the direction opposite to that of the actual relation.
As a result, appropriate learning and mislearning are repeated to greatly fluctuate the stored throttle learning value. Thus, there arises a problem that a deviation is generated in the throttle opening for obtaining the target amount of intake air, which prevents the target amount of intake air from being achieved.